108 



NUTRITION. 



merely by investigating the fragment of a tooth under a mi- 

 croscope. 



222. Another process, subsidiary to digestion, is called 

 insalivation. Animals which masticate their food have 

 glands, in the neighborhood of the mouth, which secrete a 

 fluid called saliva. This fluid mingles with the food as it is 

 chewed, and prepares it also to be more readily swallowed. 

 The salivary glands are generally wanting, or rudimentary, 

 or otherwise modified, in animals which swallow their food 

 without mastication. After it has been masticated and min- 

 gled with saliva, it is moved backwards by the tongue, and 

 passes down through the oesophagus, into the stomach. This 

 act is called deglutition or swallowing. 



223. The wisdom and skill of the Creator is strikingly 

 illustrated in the means he has afforded to every creature for 

 securing the means for subsistence. Some animals have 

 no ability to move from place to place, but are fixed to the 

 soil ; as the oyster, the polyp, &c. These are dependent for 

 subsistence upon such food as may stray or float near, and 

 they have the means of securing it when it comes within 

 their reach. The oyster closes its shell, and thus entraps its 

 prey ; the polyp has flexible arms, (Fig. 77,) capable of 



great extension, which it throws instantly 

 around any minute animal that comes in con- 

 tact with it. The cuttle-fish, also, has elongated 

 arms about the mouth, furnished with ranges 

 of suckers, by which it secures its prey, 

 (Fig. 47.) 



224. Some are provided with instruments 

 Fig. 77. f or extracting food from places which would 

 be otherwise inaccessible. Some of the mollusks, with their 

 rasp-like tongue, (Fig. 58,) perforate the shells of other ani- 

 mals, and thus reach and extract the inhabitant. Insects 

 have various piercers, suckers, or a protractile tongue for the 



